When soil is placed during the construction process at a location where a future structure shall reside, it is common engineering practice to test the soil for compaction and moisture content. The compaction (relative density) and moisture content is verified to ensure adequate and sustainable bearing capacity for whatever structure will be built on it.
Many test methods have been created and utilized to determine compaction and moisture at a construction site, but one of the most accurate, quickest and common methods has become the use of a field nuclear density gauge. The nuclear gauge method starts by pounding a rod (typically around ¾ inches in diameter) into the ground approximately twelve inches. After the rod has been pounded into the ground, the operator has a tool that clamps onto the top of the rod. With manual twisting and pulling motions, the operator retracts the rod from the ground. The remaining hole is used as an encasement for the nuclear gauges source probe, which is inserted into the hole to run the test.
Current rod extractors typically consist of a simple two-handed tool that latches onto the top of the rod, allowing the rod to be manually twisted and pulled up at the same time. This process is relatively non-strenuous when sands or granular soils are encountered, but more clayey soils, especially lean or fat clays, exert much more sidewall force and friction upon the rod, making it very strenuous and sometime dangerous to manually retract the rod from the ground. Many times the force and effort required to withdraw the rod is so high that a weaker operator will be unable to remove the pin.
When pounded fully into the ground, the top of current rods, where the tool latches on, is approximately 5 inches above the surface of the ground. Many safety regulations require that heavy lifting be done with the knees, not the back. But with current rod extraction methods, the use of the knees would not provide near the upward or torsion force required to remove the pin. The only way to provide adequate force to remove current rods is with the use of the back and arms, which unfortunately has resulted in many back injuries.
One current method offered by a few manufacturers to alleviate the effort required to remove the rod is a lengthened rod rising to about chest height. The rod is encased with a heavy collar that travels up and down the rod. A circular stationary disc is secured on top of the rod. The operator slides the hammer quickly up the rod's shaft, impacting the hammer into the upper disc. The upward impacting forces pound the rod out of the ground. This method is used for nuclear gauge tests as well as other soil tests that require the insertion of a rod or probe into the ground. This method is relatively effective for the extraction phase, but the weight of the equipment is substantially more and more effort is required to carry the heavier equipment from test location to test location. No other system is currently in use that provides mechanical advantage during rod extraction from the ground. Typically operators are required to carry the equipment by hand; therefore any rod extraction system must be relatively lightweight and compact. Because of the hammering action upon the rod, typically with a 5-pound hammer, as well as other factors inherent to construction sites, the extraction systems must also be very durable.
U.S. Pat. No. 5,931,236 to CEE, L.L.C. and U.S. Pat. No. 5,186,263 to Kejr are soil-sampling systems with a soil probe that incorporate a screw mechanism providing movement for soil penetration or separation. These inventions provide for advantages in soil sampling and provide no mechanical advantage to remove a pin, under sidewall and friction resistance, from the ground. U.S. Pat. No. 4,790,392 to Clements provides mechanical advantage in retracting a soil probe with the use of a jacking mechanism, but this type of system would be bulky and heavy, and as with the previously mentioned upward hammer system, would require additional provisions and effort if it were to be transported and carried by an operator to numerous nuclear density tests. The incorporation of moving parts would also affect its durability.